Generally, electric toothbrushes often use a mechanical switch or the like on the casing of the electric toothbrush as an input apparatus for receiving user operations. However, when a mechanical switch is used, a gap is formed between the switch unit and the casing, thus allowing foreign matter to accumulate in the gap and making cleaning difficult. Also, since space is necessary in order to dispose the mechanical switch, it is difficult to dispose the switch in a narrow portion of the casing and in a portion where other parts are disposed.
Capacitance-type touch switches and the like have been used as the input apparatus in order to resolve this problem. With this technique, electrodes are provided inside the casing, thus making it possible to separate the interior and exterior of the casing so as to achieve good waterproofing, and cost is suppressed since there is no need for fabrication or additional mechanical parts.
Examples in which a capacitance-type input apparatus is applied to a handheld device include the toothbrush with electronic melody generator in Patent Literature 1 (JP S60-114206A), the handheld instrument in Patent Literature 2 (JP 2006-520212A), and the personal care device provided with capacitive on/off switch in Patent Literature 3 (JP H5-235733A).
Since change in capacitance is used as input with a capacitance-type input apparatus, a false operation is performed when the input apparatus of a handheld device is unintentionally touched when repositioning the casing portion in the hand.
As methods for avoiding false operations due to unintentional touch, examples of methods for rejecting or recognizing input at one site based on input at another site include the method proposed in Patent Literature 4 (JP 2009-217814A) for selectively rejecting touch contact in an edge region of the touch surface, and the heating cooker proposed in Patent Literature 5 (JP 2010-266133A).